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POConnecting std::basic_ofstream<unsigned char> to a FIFO. bad_cast exceptions
 

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  1. POConnecting std::basic_ofstream<unsigned char> to a FIFO. bad_cast exceptions
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    <p>Using gcc 4.4.3 on Linux 2.6.32, I get bad_cast exceptions when connecting std::basic_ofstream to a FIFO.</p> <p>Stepping though the debugger, I can see that the error is generated at various places in the standard library because the _M_codecvt member of the stream or filebuf object is NULL. Exactly where it happens depends on the order of operations, but it appears to be the same cause in each.</p> <p>So am I doing something fundamentally stupid here? ofstream and ifstream work fine. Is there some reason that you shouldn't attach a stream of anything besides char to a FIFO? </p> <p>Thanks in advance.</p> <p>EDIT: Adding source code.</p> <pre><code>#include &lt;iostream&gt; #include &lt;fstream&gt; #include &lt;stdio.h&gt; #include &lt;sys/stat.h&gt; #include &lt;pthread.h&gt; using namespace std; //#define CHAR char #define CHAR unsigned char bool still_writing = true; void* reader (void*) { basic_ifstream&lt;CHAR&gt; in ("FIFO", fstream::in); basic_streambuf&lt;CHAR&gt; *stream_buffer = in.rdbuf(); bool no_reads = true; CHAR buffer[10]; while (stream_buffer-&gt;in_avail() || still_writing || no_reads) { in.readsome(buffer, 10); const int got = (int)in.gcount(); if (got &gt; 0) { std::cerr &lt;&lt; "Got something!\n"; no_reads = false; } } } int main () { mkfifo ("FIFO", S_IRUSR | S_IWUSR); pthread_t reader_thread_id; pthread_create (&amp;reader_thread_id, NULL, reader, NULL); basic_ofstream&lt;CHAR&gt; out ("FIFO"); out &lt;&lt; (CHAR) 70; still_writing = false; out.flush(); pthread_join (reader_thread_id, NULL); remove ("FIFO"); } </code></pre> <p>In this version, the exception arises from <code>stream_buffer-&gt;in_avail()</code> If you swap the <code>#define</code> statements, everything is fine.</p>
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    1. USMike B
    1. USMike B
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      1. POConnecting std::basic_ofstream<unsigned char> to a FIFO. bad_cast exceptions
      1. USMike B
      1. VTFavorite
    1. COHow exactly do you attach the stream? Do you have some example code?
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      1. POConnecting std::basic_ofstream<unsigned char> to a FIFO. bad_cast exceptions
      1. USsth
    2. COI've added test code. I'm just opening the FIFO with basic_(i/o)fstream.
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      1. POConnecting std::basic_ofstream<unsigned char> to a FIFO. bad_cast exceptions
      1. USMike B
    3. COMore a guess than a real answer: The stream tries to obtain an std::codecvt<unsigned char, char, mbstate_t> from the global locale, but fails to get one because the only standard codecvt's are for char and wchar_t. Workarounds: use char instead of unsigned char, or imbue the stream with a locale containing a codecvt of the right type.
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      1. POConnecting std::basic_ofstream<unsigned char> to a FIFO. bad_cast exceptions
      1. USÉric Malenfant
 

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